Hydraulic drive units including hydraulic motors are frequently used in aircraft to alter the configuration of various control surfaces such as flaps or the like. When an aircraft is in flight, aerodynamic forces acting on such control surfaces may actually act as aiding loads when the hydraulic system is being operated to change the position of the control surface. That is to say, in such cases the aerodynamic forces acting on the control surface being altered do not oppose the alteration, but rather, assist it.
When such occurs, the hydraulic motor may actually be driven by the control surface, rather than vice-versa and thus it will act as a pump. This in turn will result in the hydraulic motor pumping hydraulic fluid back toward the source of fluid under pressure. Many aircraft system designers prohibit such backflow from occurring for any of a variety of reasons. For one, filters in the supply line may be backflushed by backflow resulting from an aiding load and thus contaminate other systems that may be associated with the hydraulic fluid source.
In other systems which actually prohibit backflow, the possibility for failure of one or more system components which might disable the entire hydraulic system exists and if such failure cannot be isolated, control of the aircraft may be undermined.
Still other systems that prevent backflow act to recirculate backflow through the hydraulic motor as it acts as a pump to absorb the energy added to the system by the aiding load. Many of these systems, however, encounter overheating of the hydraulic fluid which is obviously undesirable. To avoid this possibility, the prior art has turned to the use of increased diameter hydraulic lines and/or longer hydraulic lines in the recirculation path so as to increase the volume of hydraulic fluid that is recirculated. Because the fluid quantity is increased, the energy absorbing ability of the hydraulic fluid, without overheating, is proportionately increased.
While this solution to the problem works well, it is not without drawbacks. Weight and volume constraints always exist in the design of aircraft. The increased capacity of the system increases the quantity of hydraulic fluid that must be utilized, thereby increasing weight. A weight increase is also found as a result of using a larger diameter conduit and/or longer conduits. Undesirable volume increases are also encountered as a result of the enlarged diameter of the conduits and/or increased length thereof.
The present invention is directed to overcoming one or more of the above problems.